Discussion
Many countries in tropical Asia are struggling to conduct influenza
surveillance in 2020, likely due to disruptions from the COVID-19
pandemic. However, unlike the observation in the Southern
Hemisphere1,6,7 influenza has not disappeared from
circulation, and some countries experienced a delayed resurgence of
community circulation of influenza viruses. The heterogeneity in the
magnitude of the influenza activity across countries in tropical Asia is
noteworthy and likely due to multiple factors, including surveillance
artefact, degree of travel restrictions, and adherence to COVID-19
interventions. Although data from Africa are sparse, a similar pattern
may be emerging.5 This has important implications for
the 2020-2021 Northern Hemisphere influenza season, and for future
influenza vaccine strain selection.
First, it is critical that persons recommended to receive influenza
vaccinations get vaccinated. The COVID-19 pandemic is disproportionately
impacting older persons, those with underlying chronic conditions, and
other traditionally underserved populations,8,9 many
of whom are also at increased risk of severe complications of influenza.
Influenza vaccination could prevent unnecessary added morbidity and
mortality in these target groups and may prevent health care facilities
from being overwhelmed by persons concerned that influenza-associated
respiratory symptoms may represent COVID-19 illness.
Second, maintaining surveillance and outbreak response is essential to
track the geographic spread and obtain viruses so vaccines remain
optimized to circulating influenza viruses. At the WHO Collaborating
Center for Reference and Research on Influenza at CDC Atlanta, global
surveillance submitted 583 influenza viruses to CDC between March 1 and
September 30, 2020, a 69% decrease from an average of 1,908 viruses
during the same months in the years 2015-2019. Furthermore, the limited
data from tropical Asia suggest that genetically divergent influenza
A(H3N2) viruses are currently in circulation. In Cambodia, officials
investigated outbreaks of influenza A(H3N2) viruses in semi-closed
settings in August-October 2020.10 These viruses and
some from Bangladesh, belong to a different genetic clade,
3C.2a1b+T131K, than the currently recommended 2020-2021 Northern
Hemisphere influenza vaccine virus, A/Hong Kong/267/2019, which comes
from genetic clade 3C.2a1b+135K+137F.11
The data presented here are a reminder that the low levels of influenza
circulation seen in the northern hemisphere in summer 2020 may not
necessarily persist into the upcoming influenza season, and influenza
surveillance and prevention strategies should continue as planned and
not be delayed.